1. Field of the Invention
This invention relates to a process for preparing lubricating oil basestocks. More particularly, a hydrocarbon feedstock is dewaxed by contacting the feedstock with an amorphous isomerization catalyst followed by a crystalline molecular sieve dewaxing catalyst.
2. Background of the Disclosure
In order to achieve the low temperature properties required for modern lubricating oil basestocks, it is usually necessary to dewax lubricating base oil feeds to remove waxy paraffins. It is well known that removal of waxy paraffins is needed to produce a base oil having the low pour points needed for acceptable cold flow properties.
Conventional methods for dewaxing include solvent dewaxing and catalytic dewaxing. It is difficult to economically produce a base oil which meets the low temperature properties required by present and future standards for engine oils. i.e., a high viscosity index (VI) and low pour point, from a conventional crude feedstock by solvent dewaxing alone, particularly as the VI and pour point demands are made increasingly stringent. Alternatives to solvent dewaxing include catalytic dewaxing by selective hydrocracking and/or catalytic dewaxing by wax isomerization. Both alternatives typically employ shape selective crystalline molecular sieves.
U.S. Pat. No.5,149,421 discloses a process for catalytically dewaxing a hydrocarbon feed by contacting the feed in the presence of hydrogen with a layered catalyst containing an intermediate pore size silicoaluminophosphate molecular sieve and a hydrogenation component, and an intermediate pore size aluminosilicate zeolite.
U.S. Pat. No.4,919,788 describes a process for producing a lubricating oil basestock with a target pour point and high VI by dewaxing a feed with a catalyst containing at least one large pore zeolite having a hydrogenation-dehydrogenation component to isomerize waxy paraffinic components and selectively dewaxing the effluent by preferential removal of straight chain, waxy components. The selective dewaxing component can be solvent or selective cat dewaxing. Selective cat dewaxing can be accomplished by a zeolite such as ZSM-22 or ZSM-23.
EP 188,898 B1 relates to a process for dewaxing a feedstock by contacting the feed with a crystalline zeolites having a Constraint Index less than 2 associated with a hydrogenation/dehydrogenation component in a first stage followed by contacting the effluent from the first stage with a second stage catalyst containing a crystalline zeolite having a Constraint Index greater than 2 also associated with a hydrogenation/dehydrogenation component.
WO 96/07715 describes a process for producing a high VI lubricant from a waxy feed by a process in which the waxy feed is catalytically dewaxed primarily by isomerization using a low acidity large pore zeolite isomerization catalyst containing a noble metal hydrogenation component followed by a second catalytic dewaxing step using a constrained intermediate pore crystalline molecular sieve containing a metal hydrogenation/dehydrogenation component.
EP 744,452 relates to a process for producing lubricating base oils by contacting hydrocracker bottoms with a catalyst comprising Pt and/or Pd on a refractory oxide carrier in the presence of hydrogen, separating the effluent from step 1 into a light and heavy distillate fraction and catalytically dewaxing the heavy distillate fraction.
It would be desirable to have an economic process for selectively producing a high VI, low pour point lubricating base oil under mild conditions to maximize yield and low temperature properties.
The present invention relates to a process for economically producing a lubricating oil basestock with excellent low temperature properties by dewaxing a feedstock using a first amorphous isomerization catalyst followed by a crystalline molecular sieve dewaxing catalyst. The process for producing a lubricating base oil having good low temperature properties comprises:
(1) contacting a hydrocarbon feedstock with an amorphous silica-alumina based isomerization catalyst having a pore volume less than 0.99 ml/gm (H2O), an alumina content in the range of 35-55 wt % based on silica-alumina and an isoelectric point in the range of 4.5 to 6.5, and a metal hydrogenation component in the presence of hydrogen to at least partially isomerize waxy paraffins in the hydrocarbon feedstock, and
(2) contacting at least a portion of the at least partially isomerized feedstock with a 10 or 12 ring shape selective intermediate pore crystalline molecular sieve containing a metal hydrogenation component in the presence of hydrogen to at least partially catalytically dewax the feedstock from step (1).
The isomerization catalyst and the dewaxing catalyst can be contained in a single reactor in a layered configuration provided that the feed-stock first contacts the isomerization catalyst. Alternatively, the isomerization catalyst and dewaxing catalyst may be in separate reactors provided that the feedstock first contacts the isomerization catalyst.